Miley Cyrus may be enjoying her personal sexual revolution in the spotlight, but a sexpert she is not.

On Monday, the tongue-wagging 20-year-old told Matt Lauer that people stop having sex after 40. Scott Collins detailed the cringe-worthy “Today” show interview in The Times’ Show Tracker blog:

“I heard when you turn 40 things start to go a little less sexual," Cyrus said, kicking her legs back and forth as she sat on a tall stool. “So probably around 40, around that time, I heard that’s when people don’t have sex anymore.”

Cyrus, like a lot of kids her age, is obviously ridiculous. But Cyrus is not the only woman in Hollywood worried about expiration dates.

In an interview with Esquire, Scarlett Johansson, whom the mag just named this year’s sexiest woman alive, said: “You know, I gotta hustle. I’m a 28-year-old woman in the movie business, right? […] Pretty soon the roles you’re offered all become mothers. Then they just sort of stop.”

It’s a sad commentary on how the entertainment industry treats age like a disorder, when the real world, the one outside of Hollywood, takes a different view.

But when does adulthood actually start in this day and age? We used to think our lives started at 18 or 20 — 25 at the latest. Now, the milestones we associate with growing up keep getting pushed back. Like having kids after 40 — which, according to Cyrus’ logic, would be impossible.

“Traditional signifiers of crossing into adulthood — like marriage and having kids and buying starter homes — tend to come later these days, thanks in part to sexual liberation and assisted reproductive technologies that free us to have kids much later than used to be imaginable, the Great Recession, and exorbitant housing costs and student loan debt that can keep us in the world of rentals and roommates well into our 30s and beyond,” writes Daum, who says we’ve become confused about what’s age-appropriate.

Hollywood will eventually catch up to the real world. It has to in order to keep appealing to (paying) audiences. And, in a lot of ways, it’s already making significant strides.

For the time being, it's still disheartening to hear confident female stars talk publicly about how getting older somehow means part of your life is ending.